Drinking water has been, and continues to be, heavily treated for bacteria and other microscopic organisms that may cause infection in humans and other animals subsequent to consumption. In order to disinfect water supplies, halogenated materials have been introduced therein that have proven more than adequate for such a purpose. Unfortunately, although such halogenated compounds (chlorinated and chloraminated types, primarily) exhibit excellent disinfection capabilities, when present within aqueous environments containing organic compounds at certain pH levels these halogenated compounds may generate byproducts that may themselves create health concerns. The United States Environmental Protection Agency (USEPA) in fact regulates five specific types of haloacetic acids within drinking water, monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid. Removal of such compounds from drinking water is not economically feasible thus, residual amounts may remain within treated water supplies that may require further removal processes to be undertaken. Of course, if the level of contamination is sufficiently low, initiation of such potentially expensive removal steps would be unwise from an economic perspective.
The USEPA currently has set a maximum contaminant level for the five haloacetic acids (collectively referred to as HAA5; four other haloacetic acids are currently not regulated by the USEPA, bromochloroacetic acid, bromodichloroacetic acid, dibromochloroacetic acid, and tribromoacetic acid; including these, the total haloacetic acid group is known as HAA9) at a total amount of 0.060 mg L−1 and for the trihalomethanes at 0.080 mg L−1. It is thus important to reliably analyze and measure the total amount of such contaminants in order to determine if removal or reduction is necessary.
The USEPA has instituted its own testing methods for such a purpose. One, known as EPA 552.2, involves the liquid-liquid extraction of haloacetic acids from water sources into methyl-t-butyl ether, followed by derivatization with acidic methanol to form the corresponding haloacetic acid methyl esters. Analysis by gas chromatography-electron capture detection provides reliable measurements of the haloacetic acid amounts present within the subject water supply. The other, USEPA 552.3, is a derivative of the first with optimizations of acidic methanol neutralization procedures for improvement in brominated trihalogenated haloacetic acid species. Both methods are generally robust and capable of analyzing diverse drinking water matrices for each HAA9 species with low method detection limit (MDL) values (<0.5 μg L−1) and excellent accuracy and precision values. Such values are thus of great importance for any other type of drinking water analytical method in order to ensure exactness of results so the utility may properly respond to any measured levels that are unacceptably high. If the detection limits, however, are of an improper scale, the exact levels of such disinfection byproducts may be difficult to properly measure for such a purpose and the resultant drinking water samples may be considered acceptable when, in effect, such are outside the necessary parameters.
Unfortunately, these general processes have also been found to have numerous drawbacks, however. For instance, injection port temperature can affect debromination of certain haloacetic acid species (particularly tribrominated types) that may lead to under-representation of the amount of such contaminants present within the tested water source. Likewise, the water content of the methyl-t-butyl ether extract may decarboxylate the haloacetic acids, again leading to an under-reporting of the actual amounts present within the test sample. Furthermore, the involved processing needed to actually undergo such analysis makes an on-line protocol rather difficult to implement, particularly when hourly sampling is necessary. Other derivatization methods have been either followed or suggested for gas chromatography analyses of drinking water sources as well, including utilizing diazomethane, acidic ethanol, and aniline. Such reactant-based measurements, however, all suffer the same time and labor-intensive problems as with the two EPA test procedures noted above. As such, on-line analysis through these protocols are difficult, expensive, and labor intensive to implement.
Measurement at the source (i.e., within a water purification plant location) may be effective for system-wide average readings; however, in the large supplies of water at such locations, the chances of proper sampling to that effect may be suspect since the contaminants may be present in varied locations, rather than definitively mixed throughout the tested water supply itself. Additionally, testing may not uncover the actual level of residual haloacetic acid disinfection byproducts prior to the water supply being disbursed to distant dispense sites (transfer pipes, homes, schools, businesses, etc.). In any event, there is a relatively new regulation in place that requires utilities to provide evidence of compliance with haloacetic acid levels at multiple locations, rather than a straightforward system-wide average. Thus, since the above-described derivatization procedures with gas chromatography-electron capture detection analytical methods and purge and trap gas chromatography with either previously mentioned detector are not suitable for a uniform haloacetic acid measurement scheme, there is thus a drive to implement remote testing via real-time, on-line methods for water supply HAA5, and, more importantly, for HAA9 contaminant level measurements.
A variety of testing protocols have been suggested for water utility drinking water source analytical procedures. For instance, high performance liquid chromatography, utilizing electrospray ionization-mass spectrometry or ultraviolet absorbance as the detector, has been attempted, as well as ion chromatography, with membrane-suppressed conductivity detection or, as well, ultraviolet absorbance detection. Other attempts with inductively coupled plasma-mass spectrometry and electrospray ionization-mass spectrometry coupled with ion chromatography have been followed as well for this same purpose. The detection level can be as low as 0.5 to less than 10 μg L−1 for HAA9 species, but only subsequent to sample preparations. The sensitivity and selectivity of ion chromatography and high performance liquid chromatography methods are easily sacrificed without the cumbersome preparations in place, therefore requiring operator intervention during analysis. Again, as with the USEPA methods, these issues invariably lead to serious drawbacks when on-line implementation is necessary. Attempts at implementing these measuring schemes in such a desirable on-line, remote test procedure have basically failed.
However, such a desirable on-line procedure has been achieved, to a certain extent, for the determination of both the amount and separate identification of each haloacetic acid species (within a certain degree of reliability, such a unique process allows for a rough determination in an on-line setting of the amount of each separate species present within the tested water source). Unfortunately, however, such a new test protocol does not provide a specific enough measurable result to match the necessarily effective MDL results provided by both USEPA 552.2 and 552.3 standards (which are roughly a degree of magnitude more effective). Since any measurements made along a water line must provide extremely reliable results in this manner, particularly at any point along such a line, there remains a noticeable need to increase the degree of measurement reliability for an on-line, remote system. Again, since the USEPA test standards are not effective in such settings, such a need is amplified as proper HAA5 (or HAA9) measurements are required to be as specific (and thus as reliable) to the same levels as for USEPA 552.3, at least, along the entirety of a water line to be acceptable. With the increase in water needs around the country (if not the planet), and the requirement that such water sources not only exhibit proper levels of microbe activity (essentially, or, at least, desirably, none), and thus are subject to chlorination (or chloramination) to a large degree, the need to provide a more reliable testing measure for such chlorination byproducts within a drinking water line is evident.
As well, the ability to provide such test results in an on-line, remote setting to the degree of magnitude that mirrors those obtained through the USEPA test standards should be time-effective and involve the utilization of suitable (and reliable) reagents to generate such reliable measurements. It is important to realize, too, that the USEPA standards are tedious, time consuming, and require a skillful hand for successful analysis. For instance, these procedures require over 20 consecutive steps for sample preparation, followed by a 40 minute analysis time using gas chromatography with electron capture detection (GC-ECD). Both USEPA methods excel at parallel, grab-sample analysis, but primarily where turnaround times of 1 to 2 days are acceptable. The current regulations, though, as alluded to above, require greater efficiencies such that a water utility needs to know the specific levels of HAA activity is along a water source line as soon as possible in order to effectuate the necessary additions of reagents therein to combat such carcinogenic materials immediately. As such, the USEPA tests are simply improper (and inefficient) for on-line, real-time monitoring and optimization where such immediate turn-around for concentration data is required.
The prior on-line systems that have been developed to compete with the USEPA standards utilize a post-column reaction-ion chromatography platform (PCR-IC) with two different forms of selectivity for the HAA9 species: 1) separation using an ion chromatography column and 2) reaction with nicotinamide in basic solution as post-column reagent to produce a fluorescent product. The problem with the original protocol, unfortunately, was that bromochloroacetic acid interfered with dichloro- and dibromoacetic acid quantifications. Despite this problematic limitation, it was determined that fluorescence detection provided a much improved detection protocol in comparison with ultraviolet absorbance and mass spectrometry possibilities. Thus, although such a fluorescence method of detection, coupled with the post-column reaction (again with nicotinamide reagent) and ion chromatography, exhibited the best results in terms of an on-line test method for HAA5 drinking water contaminant measurement levels, there remained a definite need for improvements in total haloacetic acid measurements and identifications within such test samples. Since then, this PCR-IC method for HAAs has been updated for determination of HAA9 species and inclusion of an on-line, internal standard calibration protocol using 2-bromobutanoic acid (2-BBA). This PCR-IC method is an efficient analyzer for on-line, real-time monitoring of the HAA9 species, and reports concentration data immediately after analysis. This protocol also does not require manual sample handling or preparation steps prior to analysis, and uses commercial, off-the-shelf components. As well, such an alternative has permitted compensation for both random and systematic errors, accounts for any signal fluctuations, and drastic reductions in calibration time.
Such a PCR-IC instrument has been extensively compared with the USEPA 552.3 standard, based particularly on MDL, accuracy, precision, and side-by-side comparison studies in real-world drinking water samples. The MDL values for the individual HAA9 species for the PCR-IC range from 1-5 μg L−1 and the USEPA MDLs range from 0.04 to 0.4 μg L−1, both with acceptable accuracy and precision as defined by the USEPA. The MDL values for the PCR-IC are generally an order of magnitude larger than the USEPA MDL values, but despite this difference, the bias between the two methods is acceptable in drinking water samples, with Total HAA9 concentrations ranging from 5 μg L−1 up to 50 μg L−1. The bias of the individual HAA9 species was found to be within a factor of 1-1.5 of the respective MDL, thus bias values for DCAA are expected to be highest since it has the highest MDL of the HAA9 species.
The empirical relationship between bias and MDL indicates that improving the MDL values of the PCR-IC analyzer will also improve the bias between PCR-IC and the USEPA 552.3 analysis. Unfortunately, such improvements have proven difficult to achieve, particularly in a manner that allows water utilities to completely (or significantly) supplant the utilization of USEPA standards as the basis of HAA measurements within drinking water supplies. Again, the ability to provide reliable, effective, and timely MDL levels for drinking water HAA concentrations, in this respect, would be highly desirable within this industry.
Of possibly even greater interest, however, is the capability of any such system to provide reliable testing results at effective time intervals. Past measuring techniques have proven effective on monthly or quarterly schedules; desired timeframes, however, as noted above, are hourly, at least, instead. The past analytical procedures discussed above, are rather difficult to employ at remote locations to begin with; to attempt testing every hour further exacerbates an already cumbersome procedure. On-line monitoring, though highly prized in the drinking water industry, has thus proven difficult to employ. Even with mobile methods in use, bench-top scale instruments have been necessary, rather than portable devices for such applications. Additionally, the reliability of any such on-line monitoring system has been highly suspect due to fluctuations in readings as calibration for short-term measuring intervals has not been easily incorporated therein, let alone actually followed.
To compound the difficulties associated with on-line monitoring systems of this type, the reliability of measurement and analysis of water samples is based upon the capability of the overall system to provide reproducible results at different times. With a standard sample provided for rather long periods of time until a new sample may be introduced within the remote system, the possibility that the standard has been altered through temperature fluctuations over time, or growth or production of undesirable organisms or chemical species therein during storage may cause problems ultimately in the resultant measurements.
There thus exists a need to provide an effective remote calibration system in order to alleviate such potential analytical disparities. To date, the best on-line, remote systems employed for such drinking water analysis at hourly intervals appear to lack the necessary degree of concentration measurements set forth by the USEPA protocols. Even with a calibrated procedure that allows for more reliable measures at different time intervals, the primary deficiency lies in the exactness of the actual measurement levels. As noted above, the MDL recordations for USEPA tests are a full magnitude below that for these prior PCR-IC test procedures, both with and without calibration steps present. Thus, again, there still remains a need to provide such an effective on-line, remote drinking water analysis process, but with measurement levels on par with USEPA results. Such a continuous system would basically involve testing procedures that are automatically undertaken remotely in regular intervals, whether by the hour, minute, day, etc. The ability to undertake remote testing and analysis permits on-line and real-time quantification and/or qualification of potential contaminants (i.e., total haloacetic acid species) with little human involvement in the overall testing procedures thus provides significant efficiencies to such overall water sample testing capabilities. In order to provide reliable data in such remote locations, there is an expressed need to provide such effective MDL measurement results within the overall testing system in order to ensure the user is provided the most exact measurements on demand at any point of the subject water line, and when the contaminants themselves are most likely present at rather low concentrations. The capability of not only providing an on-line method for such contaminant analysis, but, as well, an overall water analysis system that functions remotely, too, would thus permit the greatest level of reliability possible on which a water utility or other like entity would base its water treatment activities, particularly when based upon water samples located within transfer lines, and not solely present in a laboratory. To date, although prior water analysis methods have been attained and proposed for on-line, remote analytical purposes, the ability to provide remote water testing protocols that render highly reliable and exact measurements without human interaction or like involvement has not been provided the pertinent industries.